1. Field of the Invention
The present invention relates to a video signal processing device, an information processing system comprising this video signal processing device, and a method of processing a video signal.
2. Description of the Related Art
A conventional information processing system uses an image supply apparatus such as a personal computer, multimedia terminal, and game machine to supply a video signal and output the signal to a display device such as a monitor or a liquid crystal panel. In such a system, the configuration is such that the image supply apparatus and the display device are linked together by an analog interface, and an analog video signal from the image supply apparatus is supplied to the display device. Therefore, if it is desired to subject the supplied video signal to digital signal processing, the video signal should first be converted by an A/D converter into a digital signal. Then, the converted signal be output to the display device through a D/A converter after the signal has been subjected to the digital signal processing.
Currently, the development and implementation of a projection type of display system is in progress as one type of multimedia presentation system. To ensure that an information processing system such as this projection type of display system can be used in as many situations as possible, it is preferable to develop a system which can be connected to and compatible with all types of personal computer. However, it is unfortunately true that the clock frequencies of video signals differ between different personal computers. Thus, it is difficult to adjust the phase of a sampling clock signal used by the A/D converter, if the clock frequencies of different types of personal computer are greatly different. If it is not possible to adjust the phase of the sampling clock signal as appropriate, problems such as a dramatic deterioration in the display characteristics will occur.
One method that has been considered for implementing such a phase adjustment is to have the user manually operate a control called SYNC adjustment. Nevertheless, this operation places a large burden on the user in that it is complicated and difficult to understand. That is why it is desired to provide a system that enables simple and automatic adjustment of the phase of the sampling clock signal.